1. Field of the Invention
This invention relates to a device and process which helps a user avoid excessive heart rates and increases in body temperature during heat stress and heavy work exposures. More particularly, it relates to a device and process that measures physiological responses to work and heat stress and provides recommendations to the user in real time. Most especially, it relates to such a device and process in which the user is provided the recommendations to make an intelligent decision to control his or her exposure to the stress. It further relates to such an apparatus and process which is useful in an industrial environment.
2. Description of the Prior Art
Two approaches are conventional to avoid excessive heart rates and increases in body temperature during heat stress exposures. One is to limit the exposure through administrative controls, such as stay times. The other is to use self-determination. Stay times are usually very conservative to protect most people. Self-determination often leads an individual to overextend himself or herself.
A variety of measuring devices are known in the art for measuring exertion and related parameters. Body core temperature is a basic physiological measure of the body's response to heat stress. Rectal temperature is commonly accepted as a primary measure. Because rectal temperature is measured by an inserted probe, it is not practical or acceptable for routine evaluation of core temperature. A substitute measure is required.
Commonly used substitutes for rectal temperature are ear, esophageal, and oral temperatures. While the temperature measuring technology for these is readily available, they pose many practical problems that make them unsuitable for a personal monitor. Swallowable or ingested thermotransmitters are possible, but unsuitable because of cost, potential liability and questionable acceptability.
A commercially available device can predict body core temperature by equalizing the heat flux from the core to the surface by placing a heater on the outside. However, this device requires too much power to be fully practical in this application, and it would give erroneous results in high ambient temperatures.
Heart rate is another physiological measure that is related to work and heat stress. There are several commercially available devices to measure heart rate in work environments. The primary markets for these devices are sport, exercise and rehabilitation. While the methods and embodiments vary somewhat, the primary method of monitoring is to provide a low and high threshold for heart rate, so that an alarm can be given if heart rate goes below or above the specified window.
For industrial environments, the low threshold does not have any real purpose. The high threshold is more valuable. If a person's heart rate exceeds the threshold, an alarm can warn him or her of possible overexertion. The problem with these high threshold warnings is how to set the threshold. Workers can and do have momentary peaks of high heart rates due to sudden bursts of activity or isometric work. These peaks do not represent sustained levels of work, but they result in an alarm that would be reasonable for sustained levels of high demand. However, with a simple high threshold, there would be many alarms that do not represent significant physiological strain. The situation is further complicated by prolonged work at an intermediate level. The high threshold would miss prolonged heart rates just below the threshold that are very significant physiological strains.
Examples of prior art devices for measuring heart rates, body temperature and related parameters are disclosed in the following issued U.S. Pat. Nos.: 4,513,753, issued Apr. 30, 1985 to Tabata et al.; 4,450,843, issued May 29, 1984 to Barney et al.; 4,425,921, issued Jan. 17, 1984 to Fujisaki et al.; 4,409,985, issued Oct. 18, 1983 to Sidorenko et al.; 4,378,111, issued Mar. 29, 1983 to Tsuchida et al.; 4,367,752, issued Jan. 11, 1983 to Jimenez et al.; 4,343,315, issued Aug. 10, 1982 to O'Leary and 4,312,358, issued Jan. 26, 1982 to Barney. The state of the art is further indicated by Humen, D.P. and Boughner, D.R., "Evaluation of Commercially Available Heart Rate Monitors,"The Canadian Medical Association Journal, Vol. 131, Sept. 15, 1984, pp. 585-589 and by commercially available heart rate monitors from Computer Instruments Corporation, Hempstead, L.I., N.Y. 11550; Biosig Instruments, Inc., Champlain, N.Y. 12919 and Dak Industries, Inc., Canoga Park, CA 91304.
While the art relating to such devices is therefore a well-developed one, a need still remains for a personal monitor and process capable of meeting the demands of an industrial environment.